Properties

The Properties dialog provides a check box for each of the properties that can be calculated. If the box to the left of the property name is checked, calculations are done for that property and the values of the property are displayed in the tables. To select or unselect a property, click the left mouse button in the box.

Most thermodynamic and transport properties can be calculated. The properties that can be displayed are divided into five categories: thermodynamic properties; transport properties plus surface tension, dielectric constant, and heating values; derivatives of the thermodynamic properties (including isothermal compressibility and volume expansivity); special properties; and mixture properties.

Thermodynamic properties include temperature (T), pressure (p), density (D), volume (V), internal energy (e), enthalpy (h), entropy (s), isochoric (Cv) and isobaric (Cp) heat capacities, ideal gas isobaric heat capacity (Cp0), ratio of Cp to Cv, speed of sound (w), compressibility factor (Z=p/DRT), Joule-Thomson coefficient (JT=dT/dp at constant h), quality (q=ratio of vapor moles to total moles), 2nd virial coefficient (B), 3rd virial coefficient (C), Helmholtz energy (a), Gibbs energy (g), and heat of vaporization (hvap). Most of these properties are given on a molar or mass basis, e.g., V=volume/number of moles.

Transport properties include the thermal conductivity (ThC), viscosity (Vis), kinematic viscosity (Vis/D), thermal diffusivity (ThC/D/Cp), and Prandtl number (Vis*Cp/ThC). The surface tension, dielectric constant, and heating values are included under the transport properties menu. The gross heating value is the amount of heat produced by the complete combustion of a unit quantity of fuel, while the net heating value is obtained by subtracting the latent heat of vaporization of water vapor from the gross heating value.

Derivative thermodynamic properties include the isothermal compressibility [kappa=1/kt/p= -(dV/dp)/V at constant T], volumetric expansivity (also known as the thermal expansion coefficient) [beta=(dV/dT)/V at constant p], isentropic expansion coefficient [k=w^2*D/p=-V/p(dp/dV) at constant s], isothermal expansion coefficient [kt=D/p(dp/dD) at constant T], adiabatic compressibility [betas=1/k/p=-(dV/dp)/V at constant s], adiabatic bulk modulus [Bs=k*p=-V(dp/dV) at constant s], isothermal bulk modulus [Kt=kt*p=-V(dp/dV) at constant T], and isothermal throttling coefficient (-JT*Cp = dh/dp at constant T). Additionally, properties contained under the derivative tab include most of the common derivatives of density, pressure, temperature, and enthalpy with respect to each other. The property dp/dT [sat] is the derivative of the vapor pressure with respect to temperature. The property dh/dZ [sat] is the Waring function (as given in Ind. Eng. Chem., 46:762, 1954) and dB/dT is the derivative of the second virial coefficient with respect to temperature (B is only a function of T).

Special properties include the acoustic virial coefficients, the negative reciprocal temperature (-1/T), exergy on a flow basis (H - T0S), exergy for a closed system (H - P0V - T0S) (see Reference State about setting the exergy reference state), specific heat input [V(dh/dV) at constant P], Cv in the two-phase region (Cv2phase) (only calculated for pure fluids), supercompressibility factor (Fpv=square root of the compressibility factor at 60 F and 14.73 psia divided by the square root of the compressibility factor at T and p), critical flow factor (the normalized sonic mass flux for inviscid, one-dimensional, steady, isentropic flow), and the internal pressure [T(dp/dT)-p at constant D]. The ideal gas values of density, enthalpy, entropy, Gibbs energy, and Helmholtz energy are also available (note that these are the ideal values at T and p, not the ideal values at zero pressure such as is the case with Cp0).

Mixture properties include fugacity (f), fugacity coefficients [f(i)/x(i)p], chemical potential, K value (vaporization equilibrium ratio - the ratio of the vapor mole fraction of a species to the liquid mole fraction of the species), molar mass (molecular weight), composition (on either a mole basis or mass basis), and several different excess functions (volume, energy, enthalpy, entropy, Helmholtz energy, and Gibbs energy).

Within the ‘Special’ properties tab is the ability to calculate values for metastable fluid states (such as a liquid that has been superheated beyond the saturated state). These include pressure, enthalpy, entropy, Helmholtz energy, Gibbs energy, and compressibility factor. For single phase states, the values of these properties will be identical to those calculated under the ‘Thermodynamic’ properties tab. However, in the two-phase region, the values given are the metastable fluid states, or more precisely, the properties calculated from the equation of state at the given temperature and density. The easiest way to generate these values is to calculate an isotherm in the Isoproperty Tables command, varying the density. The two-phase pressure for a pure fluid, calculated from the equation of state, can also be viewed by plotting a p-d diagram with the ‘Show 2-phase’ option checked.

The ‘Bulk, liquid, and vapor properties’ option displays three columns for most properties during calculations. The first column gives the overall, or bulk, value of the property, the second shows the properties of the liquid phase, and the third column gives the properties of the vapor phase. This is generally useful only when calculating state points within the two-phase region, such as a temperature and a two-phase density.

Several properties can only be calculated at the saturation states, such as the heat of vaporization and surface tension. Other properties, such as heat capacities and sound speeds, are not available in the two-phase region since they are not thermodynamically defined for two-phase states. However, the property Cv2phase is available, but its definition is quite different from that of Cv, and the two properties are discontinuous at the saturated state.

The properties are saved with other Preferences when the Save Current Options command is issued. They are restored to a previously saved option with the Retrieve Options command, or Open command.

References for the equations that calculate all of these properties can be found in the fluid information screen, with one exception: the dielectric constant. The equations for this property are documented in: Harvey, A.H., Lemmon, E.W. Method for Estimating the Dielectric Constant of Natural Gas Mixtures, Int. J. Thermophys., 26(1):31-46, 2005, https://doi.org/10.1007/s10765-005-2351-5 and Harvey, A.H., Mountain, R.D., Correlations for the Dielectric Constants of H2S, SO2, and SF6, Int. J. Thermophys., 38, 2017, https://doi.org/10.1007/s10765-017-2279-6